Set of shortest cycles through each vertex.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Edge short cycles.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Check null on MCB constructor.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>